Silica (SiO.sub.2) films formed by vacuum processes such as CVD have conventionally been widely used frequently as interlayer dielectrics in semiconductor elements, etc. In recent years, a coating-type insulating film comprising a hydrolyzate of a tetraalkoxysilane as a main component, which is called an SOG (spin-on-glass) film has come to be used for the purpose of forming a further uniform interlayer dielectric. Furthermore, with the increase in the degree of integration in semiconductor elements and the like, an interlayer dielectric having low dielectric constant comprising an organopolysiloxane as a main component, which is called an organic SOG film has been developed.
However, further excellent electrical insulation between conductors is required for higher degree of integration in semiconductor elements and the like. Consequently, an interlayer dielectric material attaining lower dielectric constant has come to be desired.
Under these circumstances, JP-A-6-181201 (the term "JP-A" as used therein means an "unexamined published Japanese patent application") discloses as an interlayer dielectric material, a coating composition for forming an insulating film having lower dielectric constant. This coating composition has an object to provide an insulating film for semiconductor devices which has low water absorption and excellent crack resistance. This prior art coating composition for insulating film formation comprises as the main component an oligomer having a number-average molecular weight of 500 or higher, obtained by polycondensating an organometallic compound containing at least one element selected from titanium, zirconium, niobium, and tantalum with an organosilicon compound having at least one alkoxy group in the molecule.
The above JP-A reference discloses the use of methanol, ethanol, 2-propanol, THF, dioxane, diethylene glycol monomethyl ether acetate or the like as a reaction solvent used for the above coating fluid for insulating film formation and the use of 2-propanol, butyl acetate or the like as a solvent for dissolving the oligomer.
WO 96/00758 discloses a coating material for silica-based insulating film formation, comprising alkoxysilanes, alkoxides of metals other than silane, and an organic solvent, which is used for forming interlayer dielectrics of a multilayered wiring board. This coating material makes it possible to coat in a large thickness, and is excellent in resistance to oxygen plasma ashing.
The above WO reference discloses as examples of the organic solvent used in the above coating material for insulating film formation, monohydric alcohols such as methyl alcohol, ethyl alcohol or isopropyl alcohol, and esters of those alcohols; polyhydric alcohols such as ethylene glycol or glycerol, and ethers or esters of those alcohols; and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone or acetylacetone.
Further, JP-A-3-20377 discloses a coating liquid for oxide film formation which is useful for surface smoothing, interlayer insulation, and other purposes in electronic parts, etc. This coating liquid for oxide film formation has an object to provide a uniform coating liquid free from formation of gelled materials and also has an object to obtain a good oxide coating film free from cracks even when curing at high temperature and treatment with an oxygen plasma are conducted. This coating liquid for oxide film formation is a liquid obtained by hydrolyzing a given silane compound and a given chelate compound in the presence of an organic solvent, and polymerizing.
This JP-A reference discloses as examples of the organic solvent used for the above composition for coating film formation, methanol, ethanol, isopropyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, propylene glycol monopropyl ether, dipropylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monobutyl ether acetate, ethylene glycol diacetate, N,N-dimethylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone.
However, none of the conventional compositions described above can form a film having a satisfactory dielectric constant or have a well balanced combination of storage stability, adhesion to substrates, uniformity of coating film, etc.